When coating automobile bodies or the like, a coating method has been conventionally used by which a primer paint is initially coated by electrodeposition on the automobile body and cured by baking, and then an interlayer paint is coated on the cured prime coating film and cured by baking, the so-called metallic paint including metallic pigments is coated as a top coating on the cured interlayer coating film, a clear paint is then overcoated in a wet-on-wet state without curing the metallic paint, and the uncured metallic paint layer and clear paint layer are then cured at the same time. In recent years, a three-wet coating method in which three layers, namely, an interlayer, a metallic paint layer, and a clear paint layer are cured by baking at the same time has been also put to practical used. A cured multilayer coating film formed by such a method is required to demonstrate excellent coating film appearance due to satisfactory orientation of flaky metallic pigments such as aluminum contained in the metallic coating film. However, the drawback of the conventional wet-on-wet method is that the uncured metallic paint layer and the uncured clear paint layer are mixed with each other at the time of coating, thereby degrading the orientation of metallic pigment particles in the cured multilayer coating film and decreasing gloss (the so-called “return unevenness”). Further, in three-wet coating, it is also required to omit or shorten a preheating step, that is, drying step, in order to reduce the release of CO2 and save energy.
A method of compounding urethane-crosslinked fine particles with a paint (PTL 1 and 2), a method of compounding a diester compound with a paint (PTL 3), a method of compounding an ethylene-α-olefin random copolymer with a paint (PTL 4), and a method of compounding a polyvalent amine polymer with a paint (PTL 5) have been used as means for preventing the wet paint layers from mixing with each other.